1. Field of the Invention
An embodiment of the present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.
2. Description of the Related Art
Different characteristics are required for transistors that are used in semiconductor devices, display devices, and the like, depending on the purpose or function of the semiconductor devices, the display devices, and the like. In order to satisfy the requirements, it is important to control characteristics of transistors, and a technique of manufacturing transistors having characteristics suited for their intended use has been researched.
As a transistor structure for reducing off-state current, a technique to provide a lightly doped drain (LDD) structure is known. In the LDD structure, a region to which an impurity element is added at a low concentration is provided between a channel formation region and a source region or a drain region, and that region is referred to as an LDD region.
There has been a report of a technique to form the LDD structure in a semiconductor layer in a self-aligned manner through, for example, a method in which stacked conductive layers to be a gate electrode are processed into a tapered shape or the like and an impurity element is added using the shape (e.g., see Patent Document 1).